[aprssig] RE: GBAS

Robert Kirk isobar at bcpl.net
Sun Feb 10 12:42:08 CST 2008

At 05:20 AM 2/10/2008, you wrote:
>What would be cool is if APRS supported an error correction uplink capability
>You would need a DGPS capable input GPS

Tom Clark W3IWI did just that 10 or more years ago in the Washington DC 
area, long before WAAS & GBAS, and while selective availability was still 
in effect.

He had access to precision GPS corrections (from his job at NASA)  and 
broadcast a  one line dgps message about once a minute over the regular 
APRS frequency. The message would go thru your TNC into your GPS and 
correct your position to WAAS class accuracy.  It worked like a charm, well 
before the Coast Guard's ill-fated DGPS program. I could pilot my boat with 

It was experimental and didn't last long for a number of reasons (One 19th 
century curmudgeon, WB..something or other, for instance, didn't like the 
once a minute transmissions clobbering his bandwidth :-), but it was a real 

Bob Kirk
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